Pockels cell

ABSTRACT

The invention relates to a pockels cell comprising two spaced-apart cuboidal RTP crystals that have a square cross section, are located one behind another, and are oriented towards each other so as to provide thermal compensation in the direction of radiation. Each of said RTP crystals is provided with electrodes on two opposite faces, said faces of one crystal being rotated by 90° relative to the faces of the other crystal and relative to the direction of radiation ( 5 ). Flexible, electrically insulating, high voltage-proof plastic mats which conduct heat well and rest against the inside of a cooling member are provided around the exterior faces of the electrodes.

The invention relates to a Pockels cell in accordance with the preamble to the main claim, that is, with two successive preferably identical parallelepiped RTP crystals that are oriented in the direction of radiation for thermal compensation to one another, that are arranged spaced from one another, and that have a rectangular cross-section, of which each is provided with electrodes on two opposing surfaces, whereby these surfaces of the one crystal are rotated by 90° to those of the other crystal with respect to the direction of radiation.

Such Pockels cells acting as electrooptical switches are known in and of themselves. The optical successive arrangement is necessary in order to eliminate the temperature-dependent effect of the double refraction and is known in and of itself. When voltage is applied to the electrodes, the electrooptically induced phase displacements are summed, and during the half wave voltage the direction of polarization at the output of the crystal arrangement is rotated 90° relative to the direction at the input, which effects the desired—optical—switching effect.

However, in these known Pockels cells it is disadvantageous that the thermal compensation only functions when the preferably identical crystals have exactly the same length. Once the crystals absorb a portion of the laser radiation that falls in the direction of radiation, it is converted locally to heat energy and leads to an increase in the temperature, which can lead to a situation in which due to a different thermal expansion the crystals are not the same length, which is undesirable. In addition, differences in the design index, caused by temperature differences, along the direction of radiation in the crystals have a negative effect on the compensation effect.

The object of the invention is therefore to further develop a generic Pockels cell in accordance with the preamble to the main claim such that the thermal compensation is maintained despite the laser radiation being partially absorbed by the crystal.

This object is inventively attained in a generic Pockels cell in accordance with the preamble to the main claim by its characterizing features in that the exterior sides of the electrodes are provided with flexible, electrically insulating, high voltage-proof plastic or rubber mats that conduct heat well and in that these are adjacent to the interior side of a cooling body.

With this embodiment it is possible to carry off in the most uniform manner possible heat occurring in the crystal, this also mechanically distorting the electrodes only minimally so that as a whole both crystals have the same length despite the heat occurring in them and a most uniform possible temperature distribution occurs in them, without the electrodes mechanically distorting the crystal at the same time. The result is thus the highest degree of precise thermal compensation of the Pockels cell by the inventively provided cooling, whereby these are provided homogeneously across each of the total of four surfaces of the two crystals provided with electrodes and are symmetrical with respect to the two electrode surfaces of each crystal. At the same time, the crystals, which are also mechanically held by means of the electrodes, are held with low distortion due to the use of the flexible plastic mats. Crystals other than RTP crystals can also be used if these also require compensation due to the temperature-dependent effect of double refraction. Likewise, the successive arrangement of four crystals is inventively possible.

When in a further design the embodiment of the cooling body and the arrangement of the crystals for this are selected to be symmetrical, the result is further homogeneous cooling across the electrode surface pairs of the adjacent crystals.

This cooling is inventively enhanced in that the cooling bodies comprise copper and have cooling channels arranged running in the direction of radiation and symmetrical to one another.

It is particularly advantageous when a coolant flows antiparallel through adjacent cooling channels, which also results in homogeneous distribution of the temperature.

This effect can be further amplified in that electrodes formed from an angle section of an electrical conductor are embodied symmetrically. Each of the two electrodes comprises two parts that are point-symmetrical with respect to a point of symmetry and that are rotated 90° relative to one another about the axis of symmetry running parallel to the direction of radiation through the point of symmetry, whereby the one electrode can be embodied in parts in order to keep thermal stress to a minimum.

One skilled in the art will furthermore understand that the electrical connector for the two electrodes is insulated by each half-shell of the cooling body and passes through parallel to its separation surface, continuing the principle of symmetry and rendering beneficial uniform temperature distribution/cooling of the crystals.

Additional useful designs and further developments of the invention are characterized in the subordinate claims.

One preferred exemplary embodiment of the invention is described in greater detail in the following with reference to the drawings.

FIG. 1 a illustrates the Pockels cell with cooling body and electrodes in an exploded drawing;

FIG. 1 b illustrates a detail of the Pockels cell in accordance with FIG. 1 and in an exploded drawing from another perspective;

FIG. 2 is a partial cut-away of the Pockels cell with cooling body in accordance with FIG. 1, in the assembled condition;

FIG. 3 is a perspective rendering of the Pockels cell in accordance with FIG. 1, in a partially assembled condition;

FIG. 4 is a front elevation the Pockels cell in accordance with FIG. 1.

In FIG. 1 a, the Pockels cell is illustrated in an exploded drawing. Provided are two RTP parallelepiped crystals 6, 7 that are arranged successively in the direction of radiation 5 and spaced from one another and that have a rectangular cross-section, of which each is provided at two surfaces opposing one another with electrodes 8, 9 made of metal, whereby the surfaces of the one crystal are rotated by 90° to those of the other crystal with respect to the direction of radiation 5. The electrodes are attached to the opposing surfaces of the crystal e.g. using an adhesive.

The one of the two electrodes 8 is preferably embodied in one piece and point-symmetrical with respect to a point of symmetry 30 (FIG. 1 b), which are rotated 90° to one another about the axis of symmetry 31 running parallel to the direction of radiation 5 through the point of symmetry 30. The other electrode 9 is embodied in two pieces such that the point of symmetry 30 is spaced equidistant from the two individual parts 30 a, 30 b and axes of symmetry define two points of symmetry 8 and 9, if any.

Provided around the exterior sides of the electrodes are flexible, electrically insulating, high voltage-proof mats 10 that conduct heat well and that are made of plastic or rubber. These mats 10 are affixed via a double-sided adhesive tape 11, which is embodied electrically insulating and to conduct heat well, to the interior side 12 of a cooling body, labeled 13A, 13B overall, and therefore are situated securely against this interior side 12. The cooling body is embodied from two half shells 13A, 13B that can be joined securely to one another at their separation surface 15 while leaving free the receiving region 14 for the two crystals 6, 7 surrounded with the plastic mats 10.

The receiving region 14 of each half shell 13A, 13B has two planar support surfaces 16, 17 that are at a right angle to one another and that extend parallel to the direction of radiation 5, of which the one faces one electrode and the other faces an electrode-free surface of each crystal.

Each cooling body 13A, 13B has cooling channels 18, 19 that run parallel to the direction of radiation 5, that each have a channel axis, that have the same diameter, that are the same distance from the separation surface 15 and that are twice that distance from one another. A coolant flows through the cooling channels. The channel axis of each cooling channel 18, 19 of the two cooling bodies 13A and 13B run parallel to one another. Furthermore, the distance between each channel axis of the cooling channels 18, 19 and the associated support surface 16, 17 is the same.

Both cooling bodies comprise copper, whereby both half shells are embodied identically and form the cooling body 13 that is largely column-shaped in the exemplary embodiment illustrated. Due to the symmetrical design of the cooling channels 18, 19 of the two half shells 13A, 13B of the cooling body 13 with its support surfaces 16, 17, a uniform cooling effect is possible on the Pockels cell arranged in the interior side 12 of the cooling body.

Furthermore, each half shell 13A, 13B of the cooling body 13 is provided with a connector 20, 21 for each of the two electrodes. Each connector is embodied as a sleeve-like part and is oriented parallel to its separating surface 15 such that the one half of the sleeve is arranged in the one half shell and the other half of the sleeve is arranged in the other half shell of the cooling body. In addition, the electrical connector is advantageously arranged in the region of the free space between the two crystals that are arranged spaced from one another. By arranging the crystals 6, 7 of the Pockels cell in the two half shells 13A, 13B of the cooling body and by designing it with cooling channels and electrical connectors for the electrodes 8, 9 of the Pockels cell, uniform cooling and thus the greatest possible gradient-free temperature distribution is possible. Consequently very high efficiency is possible with thermal compensation of the two crystals. At the same time these are kept particularly low in distortion, which both prevents damage and also does not permit mechanical stresses in the crystal that have a negative effect on thermal compensation. 

1.-20. (canceled)
 21. Pockels cell comprising an assembly of two spaced apart parallelpiped RTP crystals located one behind the other in a predetermined direction of radiation which is to be applied to the Pockels cell, the crystals being oriented in the direction of radiation to provide thermal compensation relative to each other and each being of rectangular cross-section transverse of the direction of radiation, electrodes on two opposite faces of each of the crystals, said faces of one of the crystals being rotated 90° relative to said faces of the other of the crystals about an axis parallel to the direction of radiation, and flexible, electrically insulating, high voltage-resistant plastic or rubber mats which conduct heat well superposed on exterior faces of the electrodes and a cooling body substantially surrounding said assembly comprised of the crystals, the electrodes and the mats, forming a space for receiving said assembly and having surfaces adjacent the mats.
 22. Pockels cell according to claim 21, wherein the cooling body comprises two shells attachable to each other to form said cooling body substantially surrounding said assembly, said receiving space being defined by respective mutually contiguous spaces in said half shells.
 23. Pockels cell according to claim 22, further comprising respective pairs of planar support surfaces in said spaces in said half shells, said support surfaces of each said pair extending parallel and perpendicular to the radiation direction and perpendicular to each other, one of the support surfaces of each said pair facing an electrode-free face of one of the crystals and the other of the support surfaces of the same pair facing the mat on the electrode on another of the faces of the same crystal, each crystal thereby having respective faces of the supports facing electrode-free faces and facing electrodes on faces of the crystals.
 24. Pockels cell according to claim 22, wherein the shells are substantially identical and include channels for coolant extending through the half shells substantially parallel to the direction of radiation, the channels are of substantially the same configuration and same location in each of the half shells and the channels are equidistantly spaced in the cooling body as assembled from the two shells.
 25. Pockels cell according to claim 24, wherein two of said channels are in each of the half shells.
 26. Pockels cell according to claim 25, wherein the channels are arranged for flow of coolant in the channels in opposing directions.
 27. Pockels cell according to claim 21, wherein the body comprises copper.
 28. Pockels cell according to claim 21, wherein the body comprises a hollow cylinder.
 29. Pockels cell according to claim 21, wherein the mats are adhered to the electrodes by adhesive that is highly heat conducting.
 30. Pockels cell according to claim 23, wherein the support surfaces which face the mats are adhered to said mats by adhesive.
 31. Pockels cell according to claim 23, wherein the support surfaces which face the mats are adhered to the mats by tape having adhesive on opposite faces thereof, the tape being electrically insulating, high voltage-resistant and highly heat conducting.
 32. Pockels cell according to claim 21, wherein the mats are superposed also on electrode-free faces of the crystals.
 33. Pockels cell according to claim 21, wherein the electrodes are two in number, each of the electrodes being on one face of each of the crystals.
 34. Pockels cell according to claim 32, wherein the electrodes are identical. 